Current lighting technology includes a number of different types of light sources, such as incandescent bulbs and various versions thereof, such a halogen and xenon bulbs, and flourescent tubes and bulbs, including compart fluorescent lamps (CFLs). One of the more recent light sources is light emitting diodes (LEDs) which have been, for a number of years, used for a variety of purposes. In particular, LEDs have been developed and used for lighting purposes of all types including general area and spot lighting and special purpose lighting applications, such as architectural lighting.
Such LED lighting fixtures typically include an LED or an array of white and/or red, green and blue LEDs wherein, the type and number of LEDs depend upon the desired output light spectrum and illumination output power of the fixture. The array or LEDs will often be linear but may be circular or of any other desired orientation or shape chosen to provide the desired light emission pattern. The LEDs are typically mounted onto a printed circuit board, together with a power supply unit and, in some fixtures, control circuitry that controls the illumination and the power output levels of the individual LEDs are included. The circuit board provides mechanical support for and interconnections between the LEDs, the power supply unit and the control circuitry, typically by soldered or bonded connections, and the assembly of the LED array, the power supply and the control circuitry is mounted into a casing that includes an optical enclosure.
LED lighting fixtures, however, typically have a number of associated problems which tend to limit generally their use in lighting fixtures. For example, the range of variation in the output power levels and even the output spectrums of the LEDs of a given type are often significantly greater than the variations found, for example, in conventional light sources, such as incandescent bulbs. Due to the tolerances of the LEDs with regard to degree Kelvin temperature, the LEDs on a printed circuit board strip typically do not have precisely or exactly the same brightness and/or color over the entire length of the strip. This problem, which is a function of the Kelvin temperature tolerances of the individual LEDs and which is often referred to as the “Kelvin variation”, increases with the power output level of the LEDs and is particularly noticeable with high-power LEDs, which are otherwise particularly advantageous for use in general lighting fixtures because of their significantly higher per unit illumination power output. As a result of the variations in light output power and spectrum, that is, brightness and light color, the light output from an LED fixture is often of noticeable lower quality than the light output of a more conventional fixture, such as a fixture using incandescent or fluorescent elements. While these problems may be addressed, for example, by pretesting, sorting and/or selecting the LEDs to obtain sets of LEDs having more uniform characteristics, such methods significantly increase the associated time and costs in fabricating LED lighting fixtures which, in turn, leads to increased production costs.
Further, a commonly occurring problem for LED lighting fixtures arise from the light emission patterns of the LEDs. That is, light is emitted from the LEDs in a “spot-light beam” pattern, that is, in a conical or beam-like pattern having a relatively narrow emission angle, resulting in a light emission pattern having a relatively narrow central zone with high light level surrounded by a circular zone wherein the light level tapers rapidly off to zero. By comparison, a more conventional light source, such as an incandescent or fluorescent light source, more generally approximates a point or a linear light source and thus provides a generally uniform level of light emission over a generally spherical or cylindrical pattern.
The overlapping or adjoining light emission patterns of adjacent individual LEDs of an array of LEDs in a LED fixture thereby typically result in a light emission pattern for the fixture having a “scalloping effect.” A “scalloping effect” is most commonly described as, an overall light emission pattern comprising, at least in part, a repeating pattern of adjacent lighter and darker illumination regions wherein each region is circular or forms a part of a circle.
The LED lighting fixtures of the prior art have attempted to eliminate the scalloping effect by various techniques and methods, but such methods significantly increase the cost and complexity of the LED fixtures. In addition, while such methods of the prior art can, for example, widen the beam emitted by an LED element or array to a certain limited degree, such methods still cannot achieve a generally uniform wide area light emission pattern of a more conventional point or linear light source, such as an incandescent or a fluorescent element, and, such methods typically reduce the emitted light level of the LED element or array by absorbing at least a part of the light emitted from the LEDs.
A still further problem of LED light fixtures is that, as described above, such fixtures comprise a relatively large number of components, such as an array of LEDs, a power supply unit, control circuitry, a printed circuit board providing mechanical support for and interconnections between the LEDs, a power supply unit and control circuits, and a casing that includes an optical enclosure and/or beam shaping elements. The assembly of these components into a lighting fixture of a reasonable or acceptable size often proves to be somewhat difficult as dimensions and shape factors imposes a number of design restrictions, such as mounting the components to the printed circuit board and making circuit connections typically by soldered or bonded connections. Other restrictions imposes by size and the form factor constraints may include, for example, close and interlocking packing of the components that, in turn, require that the components be assembled or disassembled in a fixed order rather than being individually accessible.
Such component assembly restrictions, in turn, result in still further problems, such as local heat build-up with a consequential increase in the component failure rate due to the lack of adequate cooling. Such restrictions also significantly increase the difficulty, time and costs required to remove and replace failed component(s) due to the need to remove one or more components to access the failed component(s) and the need to unsolder and/or unbond connections in order to remove the failed component(s), and the reversal of the steps following replacement of the failed component(s).
The present invention provides a solution to these and other related problems associated with the prior art.